I use both ex-pens and NIC cubes at my house – the advantage to the NIC cubes being that you can build multiple levels. That could definitely be a big problem though if they are chewing through the zip ties – were they the really big zip ties like Beka was talking about? My bunnies have not ever chewed their zip ties before, thats a pretty smart bunny to figure that out
The good thing about expens is that they can be shaped different ways, and are very move-able and can be shaped to fit different areas.
That being said, I know the Leithpetwerks cages are pricey, but I do have several friends that have them and are very happy with them. They do very good workmanship. I’ve looked into buying one before, we couldn’t afford it but we did really like the style. As far as buying the amenities that go with them, the urine guard is really only necessary if your bunny tends to pee over the corner of the litter box. Chew guards could probably be a good idea though…my bunnies chew pretty much anything and if I was going to spend a good amount on a cage I’d probably want to protect it a little bit.